Japanese Patent Laid-Open No. Sho 58-47639 (JP 58-47639) describes determining whether a vehicle is traveling straight ahead or is cornering from a steering angle of handlebars, and performing turn signal cancellation when it is determined that the vehicle is travelling straight ahead.
Japanese Patent Laid-Open No. Sho 62-53256 (JP 62-53256) describes using a difference between the rotational frequencies of a front wheel and a rear wheel, which difference is involved in cornering, to determine that a vehicle is travelling straight ahead when the difference between the rotational frequencies of the front wheel and the rear wheel is small and to determine that the vehicle is cornering when the difference between the rotational frequencies of the front wheel and the rear wheel is large. This reference also describes performing motorcycle automatic turn signal cancellation on the basis of the determination results.